Location from One-Punch Man by ONE & Yusuke Murata
An underground fortress beneath Z-City — where the organized monster army planned their war on humanity before the heroes came knocking.
The Monster Association HQ was the base of operations for the largest organized monster threat the Hero Association has ever faced. Psykos designed it, Orochi ruled it, and dozens of Demon and Dragon-level monsters lived there. The S-Class raid on the Monster Association — a multi-front assault that took multiple chapters — destroyed it, but the fighting caused catastrophic surface damage to Z-City and surrounding areas.
A vast underground complex beneath Z-City with tunnels, chambers, and a throne room for Orochi. The architecture is organic and alien — walls of monster-flesh, bio-luminescent lighting, and the general aesthetic of 'what if a dungeon was designed by something that hates architecture.' It extends deep underground with multiple levels.
Also known as: Monster Association HQ, MA Base